Amorphous brazing foil
Encyclopedia
The filler metal
(FM) alloy
s that can be produced as amorphous brazing foils (ABF) are eutectic compositions formed by transition metal
s such as nickel
, iron
, copper
, etc., in combination with metalloid
s, such as silicon
, boron
and phosphorus
. In conventional crystalline state, all these materials are inherently brittle and cannot be produced in continuous forms such as foil, wire, etc. Therefore, they were available only as powders, pastes, or their derivates. On the other hand, the very presence of metalloids at or near the eutectic concentration promotes the rapid solidification (RS) conversion of such alloys into a ductile amorphous foil.
technology. Amorphous structures are characterized by the absence of a crystal lattice or a long range order. With this random, spatially uniform arrangement of the constituent atoms, their structure is similar to that of liquids.
The nature of this production process is the reason why amorphous alloys are offered only in the form of thin, ductile metal foils. Subsequently, tapes, parts and preforms can be made by e.g. slitting, cutting, stamping and etching.
material can be easily applied to the component and, in just one heating cycle, ABFs create uniform braze joints of outstanding quality.
Filler metal
A filler metal is a metal added in the making of a joint through welding, brazing, or soldering. Four types of filler metals exist—covered electrodes, bare electrode wire or rod, tubular electrode wire and welding fluxes...
(FM) alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s that can be produced as amorphous brazing foils (ABF) are eutectic compositions formed by transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
s such as nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, etc., in combination with metalloid
Metalloid
Metalloid is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, each element can usually be classified as a metal or a nonmetal. However, some elements with intermediate or mixed properties can be harder to characterize...
s, such as silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
. In conventional crystalline state, all these materials are inherently brittle and cannot be produced in continuous forms such as foil, wire, etc. Therefore, they were available only as powders, pastes, or their derivates. On the other hand, the very presence of metalloids at or near the eutectic concentration promotes the rapid solidification (RS) conversion of such alloys into a ductile amorphous foil.
Production
The production of amorphous alloys requires a manufacturing technology that operates on the basis of the necessary cooling rates, which is known as rapid solidification, or melt spinningMelt spinning
Melt spinning is a technique used for rapid cooling of liquids. A wheel is cooled internally, usually by water or liquid nitrogen, and rotated. A thin stream of liquid is then dripped onto the wheel and cooled, causing rapid solidification. This technique is used to develop materials that require...
technology. Amorphous structures are characterized by the absence of a crystal lattice or a long range order. With this random, spatially uniform arrangement of the constituent atoms, their structure is similar to that of liquids.
The nature of this production process is the reason why amorphous alloys are offered only in the form of thin, ductile metal foils. Subsequently, tapes, parts and preforms can be made by e.g. slitting, cutting, stamping and etching.
Properties
Amorphous brazing foils are compositionally much more uniform even after crystallization, they melt over a narrow temperature range under transient heating. This is a consequence of the shorter distances over which atoms of different elements have to diffuse in order to form a uniform liquid phase. The resulting instant melting and their superior flow characteristic is only one of the important features of ABFs. The absence of the residual organic solvent bases evident in powder paste/tapes correspondingly eliminates soot formation and furnace fouling. The low level of gaseous impurities in ABFs, due to the specific characteristics of its production technology, is an attractive feature for vacuum furnace brazing.Usage
ABFs are available as strip with a width from 0.5 mm to 125 mm and a thickness from 20 µm to 50 µm. Preforms can be easily produced by using punch and die, cutting/slitting, photochemical etching, and other methods. It is simple to use foils and preforms at automatic production and assembling steps. The use of foils and preforms reduces waste and enhances manufacturing efficiency. Drying and evaporation operations, which are required with powder/paste and tape forms, are not necessary. The optimal amount of brazingBrazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
material can be easily applied to the component and, in just one heating cycle, ABFs create uniform braze joints of outstanding quality.
External links
- NICKEL-CHROMIUM-BASED AMORPHOUS BRAZING FOILS FOR CONTINUOUS FURNACE BRAZING OF STAINLESS STEEL
- New Amorphous Brazing Foils for Exhaust Gas Application
- Brazing With (NiCoCr)-B-Si Amorphous Brazing Filler Metals: Alloys, Processing, Joint Structure, Properties, Applications
- Brazing Cemented Carbides: Specifics, Braze Optimization and Custom-Designed Amorphous Brazing Filler Metals
- Brazing with Amorphous Foil Preforms